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Abstract:

The present invention ensures excellent optical characteristics
corresponding with a high pixel imaging element while an imaging lens is
miniaturized and has a larger aperture.
The imaging lens includes, in order from an object side: a first lens
having positive refractive power; a second lens in a meniscus shape
including a concave surface facing an image side and having negative
refractive power; a third lens having positive refractive power; a fourth
lens in a meniscus shape including a concave surface facing the object
side and having positive refractive power in the vicinity of an optical
axis; and a fifth lens having negative refractive power in the vicinity
of the optical axis and having positive refractive power in a peripheral
section.

Claims:

1. An imaging lens comprising, in order from an object side: a first lens
having positive refractive power; a second lens in a meniscus shape
including a concave surface facing an image side and having negative
refractive power; a third lens in a bioconvex shape having positive
refractive power in a vicinity of an optical axis; a fourth lens in a
meniscus shape including a concave surface facing the object side and
having positive refractive power in the vicinity of the optical axis; and
a fifth lens formed in a meniscus shape including a concave surface
facing the image side and having negative refractive power in the
vicinity of the optical axis, and having positive refractive power in a
peripheral section.

2. The imaging lens according to claim 1, wherein all of the first to
fifth lenses are formed by lenses made of resin, and formed so as to
satisfy a conditional expression (1), a conditional expression (2), a
conditional expression (3), and a conditional expression (4) in the
following: ν1>50 (1) ν2<30 (2) ν3>50 (3)
ν4>50 (4) where ν1 is an Abbe number of the first lens at a
d-line (wavelength of 587.6 nm), ν2 is an Abbe number of the second
lens at the d-line (wavelength of 587.6 nm), ν3 is an Abbe number of
the third lens at the d-line (wavelength of 587.6 nm), and ν4 is an
Abbe number of the fourth lens at the d-line (wavelength of 587.6 nm).

3. The imaging lens according to claim 1, wherein a conditional
expression (5) in the following is satisfied:
0<f3/f4<3.0 (5) where f3 is a focal length of the
third lens, and f4 is a focal length of the fourth lens.

4. The imaging lens according to claim 1, wherein a conditional
expression (6) in the following is satisfied:
0.5<|f1/f2|<1.3 (6) where f1 is a focal length of
the first lens, and f2 is a focal length of the second lens.

5. The imaging lens according to claim 1, wherein a conditional
expression (8) and a conditional expression (9) in the following are
satisfied: 0.5<|f5/f|<3.0 (8) ν5>50 (9) where f is a
focal length of an entire lens system, f5 is a focal length of the
fifth lens, and ν5 is an Abbe number of the fifth lens at a d-line
(wavelength of 587.6 nm).

6. The imaging lens according to claim 1, wherein an aperture stop for
adjusting an amount of light is disposed nearer to the object side than
an object side surface of the second lens.

7. An imaging device comprising: an imaging lens; and an imaging element
for converting an optical image formed by the imaging lens into an
electric signal; wherein the imaging lens includes, in order from an
object side, a first lens having positive refractive power, a second lens
in a meniscus shape including a concave surface facing an image side and
having negative refractive power, a third lens in a biconvex shape having
positive refractive power in a vicinity of an optical axis, a fourth lens
in a meniscus shape including a concave surface facing the object side
and having positive refractive power in the vicinity of the optical axis,
and a fifth lens formed in a meniscus shape including a concave surface
facing the image side and having negative refractive power in the
vicinity of the optical axis, and having positive refractive power in a
peripheral section.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an imaging lens and an imaging
device, and is suitable for application to an imaging lens having a large
aperture with an F-number of about 2.0, for example, and is suitable for
application to an imaging device of small size such as a digital still
camera, a portable telephone provided with a camera, or the like using a
solid-state imaging element such as a CCD (Charge Coupled Device), a CMOS
(Complementary Metal Oxide Semiconductor), or the like.

BACKGROUND ART

[0002] Conventionally, portable telephones provided with a camera and
digital still cameras including an imaging device using a solid-state
imaging element such as a CCD, a CMOS, or the like are known. Such an
imaging device is desired to be further miniaturized, and an imaging lens
incorporated in the imaging device is also desired to have a small size
and a short total length.

[0003] In addition, recently, small-sized imaging apparatuses such as
portable telephones provided with a camera and the like have also been
miniaturized and increased in the number of pixels of an imaging element,
and models including a high pixel imaging element having eight million
pixels or more, for example, have spread.

[0004] On the other hand, such an imaging device is desired to have a fast
lens with a larger aperture in order to prevent a decrease in sensitivity
of the imaging element and an increase in noise due to a reduction in
cell pitch.

[0005] Imaging lenses of a four-piece configuration are now mainstream as
such a small-size and high-performance imaging lens (see for example
Patent Document 1 and Patent Document 2).

CITATION LIST

Patent Literature

[PTL 1]

[0006] Japanese Patent Laid-Open No. 2009-265245

[PTL 2]

[0006]

[0007] Japanese Patent Laid-Open No. 2010-49113

SUMMARY

[0008] Imaging lenses according to Patent Document 1 and Patent Document 2
are imaging lenses of a four-piece configuration corresponding with a
current high pixel imaging element, and have a small size and ensure high
optical performance by correcting various aberrations in a well-balanced
manner while a total optical length is reduced.

[0009] However, Patent Document 1 and Patent Document 2 optimize the
optical performance and the total optical length using an imaging lens
with an F-number of about 2.8. When the aperture is enlarged from the
F-number of about 2.8 to an F-number of about 2.0 with such a
configuration unchanged, spherical aberration of axial aberrations,
comatic aberration of off-axis aberrations, and field curvature are
corrected insufficiently, and it is thus difficult to ensure necessary
optical performance.

[0010] In addition, axial chromatic aberration needs to be suppressed more
for further improvement in optical performance. However, with the
configurations described in Patent Document 1 and Patent Document 2, it
is difficult to correct axial chromatic aberration while reducing the
total optical length, and it is difficult to ensure high resolution
performance necessary as the aperture is enlarged.

[0011] The present invention has been made in view of the above points,
and is to propose a small-size and large-aperture imaging lens having
excellent optical characteristics corresponding with a high pixel imaging
element and an imaging device using the imaging lens.

[0012] In order to solve such problems, according to the present
invention, there is provided an imaging lens including, in order from an
object side: a first lens having positive refractive power; a second lens
in a meniscus shape including a concave surface facing an image side and
having negative refractive power; a third lens having positive refractive
power; a fourth lens in a meniscus shape including a concave surface
facing the object side and having positive refractive power in the
vicinity of an optical axis; and a fifth lens having negative refractive
power in the vicinity of the optical axis and having positive refractive
power in a peripheral section.

[0013] The imaging lens thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0014] Thereby, in the present invention, a small-size and large-aperture
imaging lens having excellent optical performance with spherical
aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature corrected in a well-balanced manner can
be formed for a high pixel imaging element.

[0015] In addition, in the present invention, a small-size and
large-aperture imaging lens having high resolution performance with axial
chromatic aberration corrected in a well-balanced manner while the total
optical length is reduced can be formed for a high pixel imaging element.

[0016] In addition, all of the first to fifth lenses of the imaging lens
according to the present invention are formed by lenses made of resin,
and formed so as to satisfy a conditional expression (1), a conditional
expression (2), a conditional expression (3), and a conditional
expression (4) in the following:

ν1>50 (1)

ν2<30 (2)

ν3>50 (3)

ν4>50 (4)

where ν1 is the Abbe number of the first lens at a d-line (wavelength
of 587.6 nm), ν2 is the Abbe number of the second lens at the d-line
(wavelength of 587.6 nm), ν3 is the Abbe number of the third lens at
the d-line (wavelength of 587.6 nm), and ν4 is the Abbe number of the
fourth lens at the d-line (wavelength of 587.6 nm).

[0017] The conditional expression (1) defines the Abbe number of the first
lens at the d-line. The conditional expression (2) defines the Abbe
number of the second lens at the d-line. The conditional expression (3)
defines the Abbe number of the third lens at the d-line. The conditional
expression (4) defines the Abbe number of the fourth lens at the d-line.
The conditional expressions represent conditions for excellently
correcting chromatic aberration occurring in the lens system.

[0018] When the imaging lens deviates from the specified values of the
conditional expression (1), the conditional expression (2), the
conditional expression (3), and the conditional expression (4), the
correction of axial chromatic aberration, which is necessary in enlarging
the aperture with an F-number of about 2.0, becomes difficult.

[0019] Thus, in the imaging lens according to the present invention, by
satisfying the conditional expression (1), the conditional expression
(2), the conditional expression (3), and the conditional expression (4),
it is possible to reduce the total optical length while effectively
correcting axial chromatic aberration and ensuring excellent optical
performance.

[0020] Further, because all the lenses in the imaging lens according to
the present invention are formed by lenses made of resin as a same
material, amounts of change in refractive power in all the lenses at a
time of a variation in temperature can be made to be uniform, and thus
variation in field curvature, which becomes a problem at a time of a
variation in temperature, can be suppressed.

[0021] In addition, because all of the lenses in the imaging lens
according to the present invention are formed by inexpensive and
lightweight lenses made of resin, the imaging lens as a whole can be
reduced in weight while mass productivity is ensured.

[0022] Further, the imaging lens according to the present invention is
formed so as to satisfy a conditional expression (5) in the following:

0<f3/f4<3.0 (5)

where f3 is the focal length of the third lens, and f4 is the
focal length of the fourth lens.

[0023] The conditional expression (5) defines a ratio between the focal
length f3 of the third lens and the focal length f4 of the
fourth lens, and limits a balance between the refractive power of the
third lens and the refractive power of the fourth lens.

[0024] When the imaging lens deviates from the upper limit value of the
conditional expression (5), the power (refractive power) of the third
lens becomes too weak, and the correction of axial chromatic aberration
becomes difficult, so that excellent optical performance cannot be
maintained. When the imaging lens deviates from the lower limit value, on
the other hand, the power of the third lens becomes strong, which is
advantageous in terms of aberration correction, but the power of the
fourth lens becomes too weak, and the total optical length is increased,
so that the miniaturization of the present lens system becomes difficult.

[0025] Thus, in the imaging lens, by satisfying the conditional expression
(5), it is possible to reduce the total optical length while effectively
correcting axial chromatic aberration and ensuring excellent optical
performance.

[0026] Further, the imaging lens according to the present invention is
formed so as to satisfy a conditional expression (6) in the following:

0.5<|f1/f2|<1.3 (6)

where f1 is the focal length of the first lens, and f2 is the
focal length of the second lens.

[0027] The conditional expression (6) defines a ratio between the focal
length f1 of the first lens and the focal length f2 of the
second lens, and limits a balance between the refractive power of the
first lens and the refractive power of the second lens.

[0028] When the imaging lens deviates from the upper limit value of the
conditional expression (6), the power of the second lens becomes strong,
which is advantageous in terms of aberration correction, but the power of
the second lens becomes too strong, and the total optical length is
increased, so that the miniaturization of the present lens system becomes
difficult. When the imaging lens deviates from the lower limit value, on
the other hand, the power of the second lens becomes too weak, and the
correction of axial chromatic aberration becomes difficult, so that
excellent optical performance cannot be maintained.

[0029] Thus, in the imaging lens, by satisfying the conditional expression
(6), it is possible to reduce the total optical length while effectively
correcting axial chromatic aberration and ensuring excellent optical
performance.

[0030] Further, the imaging lens according to the present invention is
formed to satisfy a conditional expression (8) and a conditional
expression (9) in the following:

0.5<|f5/f|<3.0 (8)

ν5>50 (9)

where f is the focal length of the entire lens system, f5 is the
focal length of the fifth lens, and ν5 is the Abbe number of the fifth
lens at the d-line (wavelength of 587.6 nm).

[0031] The conditional expression (8) defines a ratio between the focal
length f5 of the fifth lens and the focal length f of the entire
lens system, and limits the power of the fifth lens.

[0032] When the imaging lens deviates from the upper limit value of the
conditional expression (8), the power of the fifth lens becomes weak,
which is advantageous in terms of aberration correction, but the total
optical length is increased, so that the miniaturization of the present
lens system becomes difficult. When the imaging lens deviates from the
lower limit value, on the other hand, the power of the fifth lens becomes
too strong, and it becomes difficult to correct field curvature occurring
from a center to an intermediate image height (for example a height
increased by 20 to 50 percent) in a well-balanced manner.

[0033] The conditional expression (9) defines the Abbe number of the fifth
lens at the d-line. When the Abbe number falls below the specified value,
it becomes difficult to correct axial chromatic aberration and chromatic
aberration of magnification in a well-balanced manner, and excellent
optical performance cannot be maintained.

[0034] Thus, in the imaging lens, by satisfying the conditional expression
(8) and the conditional expression (9), it is possible to reduce the
total optical length while correcting axial chromatic aberration and
chromatic aberration of magnification in a well-balanced manner and
ensuring excellent optical performance corresponding with a high pixel
imaging element.

[0035] Further, an aperture stop for adjusting an amount of light in the
imaging lens according to the present invention is disposed nearer to the
object side than the object side surface of the second lens.

[0036] Thus, in the imaging lens, an angle of incidence of a chief ray of
the imaging lens with respect to the optical axis can be decreased by
disposing the aperture stop nearer to the object side than the object
side surface of the second lens, and bringing the position of an exit
pupil as close to the object side as possible. It is thus possible to
improve light receiving efficiency, and avoid degradation in image
quality due to color mixture.

[0037] In addition, the aperture stop of the imaging lens is disposed at a
position as close to the front of the optical system as possible.
Thereby, as compared with a case in which the aperture stop is disposed
nearer to the image side than the object side surface of the second lens,
the position of the exit pupil is nearer to the front, and the total
length of the lens system can be reduced.

[0038] Further, according to the present invention, there is provided an
imaging device including: an imaging lens; and an imaging element for
converting an optical image formed by the imaging lens into an electric
signal; wherein the imaging lens includes, in order from an object side,
a first lens having positive refractive power, a second lens in a
meniscus shape including a concave surface facing an image side and
having negative refractive power, a third lens having positive refractive
power, a fourth lens in a meniscus shape including a concave surface
facing the object side and having positive refractive power in the
vicinity of an optical axis, and a fifth lens having negative refractive
power in the vicinity of the optical axis and having positive refractive
power in a peripheral section.

[0039] The imaging lens in the imaging device thus has a five-piece
configuration and a power arrangement as described above. It is thereby
possible to correct spherical aberration of axial aberrations, comatic
aberration of off-axis aberrations, and field curvature, which become a
problem when an aperture is enlarged, in a well-balanced manner, while
reducing a total optical length.

[0040] Thereby, in the present invention, the imaging device including a
small-size and large-aperture imaging lens having excellent optical
performance with spherical aberration of axial aberrations, comatic
aberration of off-axis aberrations, and field curvature corrected in a
well-balanced manner can be formed for a high pixel imaging element.

[0041] In addition, in the present invention, the imaging device including
a small-size and large-aperture imaging lens having high resolution
performance with axial chromatic aberration corrected in a well-balanced
manner while the total optical length is reduced can be formed for a high
pixel imaging element.

[0042] An imaging lens according to the present invention includes, in
order from an object side: a first lens having positive refractive power;
a second lens in a meniscus shape including a concave surface facing an
image side and having negative refractive power; a third lens having
positive refractive power; a fourth lens in a meniscus shape including a
concave surface facing the object side and having positive refractive
power in the vicinity of an optical axis; and a fifth lens having
negative refractive power in the vicinity of the optical axis and having
positive refractive power in a peripheral section.

[0043] The imaging lens thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0044] Thereby, in the present invention, a small-size and large-aperture
imaging lens having excellent optical performance with spherical
aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature corrected in a well-balanced manner can
be formed for a high pixel imaging element.

[0045] In addition, in the present invention, a small-size and
large-aperture imaging lens having high resolution performance with axial
chromatic aberration corrected in a well-balanced manner while the total
optical length is reduced can be formed for a high pixel imaging element.

[0046] An imaging device according to the present invention includes: an
imaging lens; and an imaging element for converting an optical image
formed by the imaging lens into an electric signal; wherein the imaging
lens includes, in order from an object side, a first lens having positive
refractive power, a second lens in a meniscus shape including a concave
surface facing an image side and having negative refractive power, a
third lens having positive refractive power, a fourth lens in a meniscus
shape including a concave surface facing the object side and having
positive refractive power in the vicinity of an optical axis, and a fifth
lens having negative refractive power in the vicinity of the optical axis
and having positive refractive power in a peripheral section.

[0047] The imaging lens in the imaging device thus has a five-piece
configuration and a power arrangement as described above. It is thereby
possible to correct spherical aberration of axial aberrations, comatic
aberration of off-axis aberrations, and field curvature, which become a
problem when an aperture is enlarged, in a well-balanced manner, while
reducing a total optical length.

[0048] Thereby, in the present invention, the imaging device including a
small-size and large-aperture imaging lens having excellent optical
performance with spherical aberration of axial aberrations, comatic
aberration of off-axis aberrations, and field curvature corrected in a
well-balanced manner can be formed for a high pixel imaging element.

[0049] In addition, in the present invention, the imaging device including
a small-size and large-aperture imaging lens having high resolution
performance with axial chromatic aberration corrected in a well-balanced
manner while the total optical length is reduced can be formed for a high
pixel imaging element.

BRIEF DESCRIPTION OF DRAWINGS

[0050] FIG. 1 is a schematic sectional view of a configuration of an
imaging lens in a first numerical example.

[0051] FIG. 2 is a characteristic curve diagram showing aberrations in the
first numerical example.

[0052] FIG. 3 is a schematic sectional view of a configuration of an
imaging lens in a second numerical example.

[0053] FIG. 4 is a characteristic curve diagram showing aberrations in the
second numerical example.

[0054] FIG. 5 is a schematic sectional view of a configuration of an
imaging lens in a third numerical example.

[0055] FIG. 6 is a characteristic curve diagram showing aberrations in the
third numerical example.

[0056]FIG. 7 is a schematic sectional view of a configuration of an
imaging lens in a fourth numerical example.

[0064] An imaging lens according to the present invention is formed by, in
order from an object side, a first lens having positive refractive power,
a second lens in a meniscus shape including a concave surface facing an
image side and having negative refractive power, a third lens having
positive refractive power, a fourth lens in a meniscus shape including a
concave surface facing the object side and having positive refractive
power in the vicinity of an optical axis, and a fifth lens having
negative refractive power in the vicinity of the optical axis and having
positive refractive power in a peripheral section. Incidentally, the
imaging lens has performance corresponding to a range of 24 to 40 (mm) as
focal length of the entire lens system when calculated in terms of a
35-mm film.

[0065] The imaging lens thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0066] In addition, all of the first to fifth lenses of the imaging lens
are formed by lenses made of resin, and formed so as to satisfy a
conditional expression (1), a conditional expression (2), a conditional
expression (3), and a conditional expression (4) in the following:

ν1>50 (1)

ν2<30 (2)

ν3>50 (3)

ν4>50 (4)

where ν1 is the Abbe number of the first lens at a d-line (wavelength
of 587.6 nm), ν2 is the Abbe number of the second lens at the d-line
(wavelength of 587.6 nm), ν3 is the Abbe number of the third lens at
the d-line (wavelength of 587.6 nm), and ν4 is the Abbe number of the
fourth lens at the d-line (wavelength of 587.6 nm).

[0067] The conditional expression (1) defines the Abbe number of the first
lens at the d-line. The conditional expression (2) defines the Abbe
number of the second lens at the d-line. The conditional expression (3)
defines the Abbe number of the third lens at the d-line. The conditional
expression (4) defines the Abbe number of the fourth lens at the d-line.
The conditional expressions represent conditions for excellently
correcting chromatic aberration occurring in the lens system.

[0068] When the imaging lens deviates from the specified values of the
conditional expression (1), the conditional expression (2), the
conditional expression (3), and the conditional expression (4), the
correction of axial chromatic aberration, which is necessary in enlarging
the aperture with an F-number of about 2.0, becomes difficult.

[0070] Thereby, the imaging lens has excellent optical performance
corresponding with a high pixel imaging element, and the imaging lens can
be miniaturized and have a large aperture.

[0071] Further, because all the lenses in the imaging lens are formed by
lenses made of resin as a same material, amounts of change in refractive
power in all the lenses at a time of a variation in temperature can be
made to be uniform, and thus variation in field curvature, which becomes
a problem at a time of a variation in temperature, can be suppressed.

[0072] In addition, because all of the lenses in the imaging lens are
formed by inexpensive and lightweight lenses made of resin, the imaging
lens as a whole can be reduced in weight while mass productivity is
ensured.

[0073] Further, the imaging lens is formed so as to satisfy a conditional
expression (5) in the following:

0<f3/f4<3.0 (5)

where f3 is the focal length of the third lens, and f4 is the
focal length of the fourth lens.

[0074] The conditional expression (5) defines a ratio between the focal
length f3 of the third lens and the focal length f4 of the
fourth lens, and limits a balance between the refractive power of the
third lens and the refractive power of the fourth lens.

[0075] When the imaging lens deviates from the upper limit value of the
conditional expression (5), the power (refractive power) of the third
lens becomes too weak, and the correction of axial chromatic aberration
becomes difficult, so that excellent optical performance cannot be
maintained. When the imaging lens deviates from the lower limit value, on
the other hand, the power of the third lens becomes strong, which is
advantageous in terms of aberration correction, but the power of the
fourth lens becomes too weak, and the total optical length is increased,
so that the miniaturization of the present lens system becomes difficult.

[0076] Thus, in the imaging lens, by satisfying the conditional expression
(5), it is possible to reduce the total optical length while effectively
correcting axial chromatic aberration and ensuring excellent optical
performance.

[0077] Further, the imaging lens is formed so as to satisfy a conditional
expression (6) in the following:

0.5<|f1/f2|<1.3 (6)

where f1 is the focal length of the first lens, and f2 is the
focal length of the second lens.

[0078] The conditional expression (6) defines a ratio between the focal
length f1 of the first lens and the focal length f2 of the
second lens, and limits a balance between the refractive power of the
first lens and the refractive power of the second lens.

[0079] When the imaging lens deviates from the upper limit value of the
conditional expression (6), the power of the second lens becomes strong,
which is advantageous in terms of aberration correction, but the power of
the second lens becomes too strong, and the total optical length is
increased, so that the miniaturization of the present lens system becomes
difficult. When the imaging lens deviates from the lower limit value, on
the other hand, the power of the second lens becomes too weak, and the
correction of axial chromatic aberration becomes difficult, so that
excellent optical performance cannot be maintained.

[0080] Thus, in the imaging lens, by satisfying the conditional expression
(6), it is possible to reduce the total optical length while effectively
correcting axial chromatic aberration and ensuring excellent optical
performance.

[0081] Further, the conditional expression (6) is desirably set so as to
satisfy a range shown in a conditional expression (7).

0.6<|f1/f2|<1.0 (7)

[0082] Thus, in the imaging lens, by satisfying the conditional expression
(7), the reduction of the total optical length and the correction of
axial chromatic aberration can be achieved in a better balanced manner
than in a case where the conditional expression (6) is satisfied.

[0083] Further, the imaging lens is formed to satisfy a conditional
expression (8) and a conditional expression (9) in the following:

0.5<|f5/f|<3.0 (8)

ν5>50 (9)

where f is the focal length of the entire lens system, f5 is the
focal length of the fifth lens, and ν5 is the Abbe number of the fifth
lens at the d-line (wavelength of 587.6 nm).

[0084] The conditional expression (8) defines a ratio between the focal
length f5 of the fifth lens and the focal length f of the entire
lens system, and limits the power of the fifth lens.

[0085] When the imaging lens deviates from the upper limit value of the
conditional expression (8), the power of the fifth lens becomes weak,
which is advantageous in terms of aberration correction, but the total
optical length is increased, so that the miniaturization of the present
lens system becomes difficult. When the imaging lens deviates from the
lower limit value, on the other hand, the power of the fifth lens becomes
too strong, and it becomes difficult to correct field curvature occurring
from a center to an intermediate image height (for example a height
increased by 20 to 50 percent) in a well-balanced manner.

[0086] The conditional expression (9) defines the Abbe number of the fifth
lens at the d-line. When the Abbe number falls below the specified value,
it becomes difficult to correct axial chromatic aberration and chromatic
aberration of magnification in a well-balanced manner, and excellent
optical performance cannot be maintained.

[0087] Thus, in the imaging lens, by satisfying the conditional expression
(8) and the conditional expression (9), it is possible to reduce the
total optical length while correcting axial chromatic aberration and
chromatic aberration of magnification in a well-balanced manner and
ensuring excellent optical performance corresponding with a high pixel
imaging element.

[0088] In addition, an aperture stop for adjusting an amount of light in
the imaging lens according to the present invention is disposed nearer to
the object side than the object side surface of the second lens.

[0089] Thus, in the imaging lens, an angle of incidence of a chief ray of
the imaging lens with respect to the optical axis can be decreased by
disposing the aperture stop nearer to the object side than the object
side surface of the second lens, and bringing the position of an exit
pupil as close to the object side as possible. It is thus possible to
improve light receiving efficiency, and avoid degradation in image
quality due to color mixture.

[0090] In addition, the aperture stop of the imaging lens is disposed at a
position as close to the front of the optical system as possible.
Thereby, as compared with a case in which the aperture stop is disposed
nearer to the image side than the object side surface of the second lens,
the position of the exit pupil is nearer to the front, and the total
length of the lens system can be reduced.

[0091] Thus, the imaging lens according to the present invention has
excellent optical performance, with spherical aberration of axial
aberrations, comatic aberration of off-axis aberrations, and field
curvature corrected in a well-balanced manner, for a high pixel imaging
element having eight million pixels or more, for example, even when the
aperture is enlarged to an F-number of about 2.0.

[0092] In addition, in the present invention, a small-size and
large-aperture imaging lens having high resolution performance with axial
chromatic aberration corrected in a well-balanced manner while the total
optical length is reduced can be formed for a high pixel imaging element
having eight million pixels or more, for example.

[0093] Further, because all of the lenses in the imaging lens are formed
by inexpensive lenses made of resin, variation in field curvature, which
becomes a problem at a time of a variation in temperature, can be
suppressed while mass productivity is ensured.

2. NUMERICAL EXAMPLES CORRESPONDING TO EMBODIMENT

[0094] Numerical examples in which concrete numerical values are applied
to the imaging lens according to the present invention will next be
described in the following with reference to the drawings and tables. The
meanings of symbols used in the numerical examples are as follows.

[0095] "FNo" denotes an F-number. "f" denotes the focal length of the
entire lens system. "2ω" denotes a total diagonal angle of view.
"Si" denotes an ith surface number counted from the object side. "Ri"
denotes the radius of curvature of the ith surface. "di" denotes an axial
surface interval between the ith surface and an (i+1)th surface from the
object side. "ni" denotes the index of refraction of an ith lens at the
d-line (wavelength of 587.6 nm). "νi" denotes the Abbe number of the
ith lens at the d-line (wavelength of 587.6 nm).

[0096] "ASP" in relation to the surface number denotes that the surface in
question is an aspheric surface. "∞" in relation to the radius of
curvature means that the surface in question is a plane.

[0097] Some lenses of the imaging lens used in each numerical example have
a lens surface formed in an aspheric shape. Letting "Z" be the depth of
the aspheric surface, "Y" be a height from the optical axis, "R" be a
radius of curvature, "K" be a conic constant, and "A," "B," "C," and "D"
be aspheric coefficients of a 4th order, a 6th order, an 8th order, and a
10th order, respectively, the aspheric shape is defined by the following
Equation 10.

[0098] A reference numeral 1 in FIG. 1 denotes an imaging lens in a first
numerical example corresponding as a whole to the embodiment, and has
five lenses.

[0099] The imaging lens 1 is formed by, in order from an object side, an
aperture stop STO, a first lens L1 having positive refractive power, a
second lens L2 in a meniscus shape including a concave surface facing an
image side and having negative refractive power, a third lens L3 having
positive refractive power, a fourth lens L4 in a meniscus shape including
a concave surface facing the object side and having positive refractive
power in the vicinity of an optical axis, and a fifth lens L5 having
negative refractive power in the vicinity of the optical axis and having
positive refractive power in a peripheral section.

[0100] In addition, in the imaging lens 1, a seal glass SG for protecting
an image surface IMG is disposed between the fifth lens L5 and the image
surface IMG.

[0101] The aperture stop STO in the imaging lens 1 having such a
configuration is disposed in a foremost position on the object side.

[0102] Thus, in the imaging lens 1, an angle of incidence of a chief ray
of the imaging lens 1 with respect to the optical axis can be decreased
by disposing the aperture stop STO nearer to the object side than the
object side surface of the second lens L2, and bringing the position of
an exit pupil as close to the object side as possible. It is thus
possible to improve light receiving efficiency, and avoid degradation in
image quality due to color mixture.

[0103] The imaging lens 1 thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0104] Table 1 shows lens data when concrete numerical values are applied
to the imaging lens 1 according to the first numerical example
corresponding to the embodiment together with the F-number FNo, the focal
length f of the entire lens system, and the angle of view 2ω.
Incidentally, the imaging lens 1 has performance corresponding to a focal
length of 36 (mm) when calculated in terms of a 35-mm film. In addition,
the radius of curvature Ri being ∞ in Table 1 represents a plane.

[0105] In the imaging lens 1, the surface (S2) on the object side of the
first lens L1, the surface (S3) on the image side of the first lens L1,
the surface (S4) on the object side of the second lens L2, the surface
(S5) on the image side of the second lens L2, the surface (S6) on the
object side of the third lens L3, the surface (S8) on the object side of
the fourth lens L4, the surface (S9) on the image side of the fourth lens
L4, the surface (S10) on the object side of the fifth lens L5, and the
surface (S11) on the image side of the fifth lens L5 are formed in an
aspheric shape.

[0106] In addition, in the imaging lens 1, the surface (S7) on the image
side of the third lens L3 is formed in a spherical shape.

[0107] Next, Table 2 shows the aspheric coefficients "A," "B," "C," and
"D" of the 4th order, the 6th order, the 8th order, and the 10th order of
the aspheric surfaces in the imaging lens 1 according to the first
numerical example together with the conic constant "K." Incidentally,
"E-02" in Table 2 denotes an exponential representation having a base of
10, that is, "10-2." For example, "0.12345E-05" denotes
"0.12345×10-5."

[0108] FIG. 2 shows aberrations in the imaging lens 1 according to the
first numerical example. In this astigmatism diagram, a solid line
indicates values in a sagittal image surface, and a broken line indicates
values in a meridional image surface.

[0109] Diagrams of the aberrations (a spherical aberration diagram, an
astigmatism diagram, and a distortion aberration diagram) in FIG. 2 show
that the imaging lens 1 according to the first numerical example
excellently corrects the aberrations, and has excellent image forming
performance.

[0110] Incidentally, the Abbe numbers and the focal lengths of the
respective lenses in the imaging lens 1 according to the first numerical
example are as shown in Table 3.

[0111] In FIG. 3, in which parts corresponding to those of FIG. 1 are
identified by the same reference symbols, a reference numeral 10 denotes
an imaging lens in a second numerical example as a whole, which has five
lenses also in this case.

[0112] The imaging lens 10 is formed by, in order from an object side, a
first lens L11 having positive refractive power, an aperture stop STO, a
second lens L12 in a meniscus shape including a concave surface facing an
image side and having negative refractive power, a third lens L13 having
positive refractive power, a fourth lens L14 in a meniscus shape
including a concave surface facing the object side and having positive
refractive power in the vicinity of an optical axis, and a fifth lens L15
having negative refractive power in the vicinity of the optical axis and
having positive refractive power in a peripheral section.

[0113] In addition, in the imaging lens 10, a seal glass SG for protecting
an image surface IMG is disposed between the fifth lens L15 and the image
surface IMG.

[0114] The aperture stop STO in the imaging lens 10 having such a
configuration is disposed between the first lens L11 and the second lens
L12 without being disposed in a foremost position on the object side.

[0115] The aperture stop STO of the imaging lens 10 is disposed at a
position as close to the front of the optical system as possible (nearer
to the object side than the object side surface of the second lens L12).
Thereby, as compared with a case in which the aperture stop is disposed
nearer to the image side than the object side surface of the second lens
L12, the position of an exit pupil is nearer to the front, and the total
length of the lens system can be reduced.

[0116] The imaging lens 10 thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing the total optical
length.

[0117] Table 4 shows lens data when concrete numerical values are applied
to the imaging lens 10 according to the second numerical example together
with the F-number FNo, the focal length f of the entire lens system, and
the angle of view 2ω. Incidentally, the imaging lens 10 has
performance corresponding to a focal length of 35 (mm) when calculated in
terms of a 35-mm film.

[0118] In the imaging lens 10, the surface (S1) on the object side of the
first lens L11, the surface (S2) on the image side of the first lens L11,
the surface (S4) on the object side of the second lens L12, the surface
(S5) on the image side of the second lens L12, the surface (S6) on the
object side of the third lens L13, the surface (S8) on the object side of
the fourth lens L14, the surface (S9) on the image side of the fourth
lens L14, the surface (S10) on the object side of the fifth lens L15, and
the surface (S11) on the image side of the fifth lens L15 are formed in
an aspheric shape.

[0119] In addition, in the imaging lens 10, the surface (S7) on the image
side of the third lens L13 is formed in a spherical shape.

[0120] Next, Table 5 shows the aspheric coefficients "A," "B," "C," and
"D" of the 4th order, the 6th order, the 8th order, and the 10th order of
the aspheric surfaces in the imaging lens 10 according to the second
numerical example together with the conic constant "K." Incidentally,
"E-01" in Table 5 denotes an exponential representation having a base of
10, that is, "10-1."

[0121] FIG. 4 shows aberrations in the imaging lens 10 according to the
second numerical example. Also in this astigmatism diagram, a solid line
indicates values in a sagittal image surface, and a broken line indicates
values in a meridional image surface.

[0122] Diagrams of the aberrations (a spherical aberration diagram, an
astigmatism diagram, and a distortion aberration diagram) in FIG. 4 show
that the imaging lens 10 according to the second numerical example
excellently corrects the aberrations, and has excellent image forming
performance.

[0123] Incidentally, the Abbe numbers and the focal lengths of the
respective lenses in the imaging lens 10 according to the second
numerical example are as shown in Table 6.

[0124] In FIG. 5, in which parts corresponding to those of FIG. 1 are
identified by the same reference symbols, a reference numeral 20 denotes
an imaging lens in a third numerical example as a whole, which has five
lenses also in this case.

[0125] The imaging lens 20 is formed by, in order from an object side, an
aperture stop STO, a first lens L21 having positive refractive power, a
second lens L22 in a meniscus shape including a concave surface facing an
image side and having negative refractive power, a third lens L23 having
positive refractive power, a fourth lens L24 in a meniscus shape
including a concave surface facing the object side and having positive
refractive power in the vicinity of an optical axis, and a fifth lens L25
having negative refractive power in the vicinity of the optical axis and
having positive refractive power in a peripheral section.

[0126] In addition, in the imaging lens 20, a seal glass SG for protecting
an image surface IMG is disposed between the fifth lens L25 and the image
surface IMG.

[0127] The aperture stop STO in the imaging lens 20 having such a
configuration is disposed in a foremost position on the object side.

[0128] Thus, in the imaging lens 20, an angle of incidence of a chief ray
of the imaging lens 20 with respect to the optical axis can be decreased
by disposing the aperture stop STO nearer to the object side than the
object side surface of the second lens L22, and bringing the position of
an exit pupil as close to the object side as possible. It is thus
possible to improve light receiving efficiency, and avoid degradation in
image quality due to color mixture.

[0129] The imaging lens 20 thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0130] Table 7 shows lens data when concrete numerical values are applied
to the imaging lens 20 according to the third numerical example together
with the F-number FNo, the focal length f of the entire lens system, and
the angle of view 2ω. Incidentally, the imaging lens 20 has
performance corresponding to a focal length of 30 (mm) when calculated in
terms of a 35-mm film.

[0131] In the imaging lens 20, the surface (S2) on the object side of the
first lens L21, the surface (S3) on the image side of the first lens L21,
the surface (S4) on the object side of the second lens L22, the surface
(S5) on the image side of the second lens L22, the surface (S6) on the
object side of the third lens L23, the surface (S7) on the image side of
the third lens L23, the surface (S8) on the object side of the fourth
lens L24, the surface (S9) on the image side of the fourth lens L24, the
surface (S10) on the object side of the fifth lens L25, and the surface
(S11) on the image side of the fifth lens L25 are formed in an aspheric
shape.

[0132] Next, Table 8 shows the aspheric coefficients "A," "B," "C," and
"D" of the 4th order, the 6th order, the 8th order, and the 10th order of
the aspheric surfaces in the imaging lens 20 according to the third
numerical example together with the conic constant "K." Incidentally,
"E-02" in Table 8 denotes an exponential representation having a base of
10, that is, "10-2."

[0133] FIG. 6 shows aberrations in the imaging lens 20 according to the
third numerical example. Also in this astigmatism diagram, a solid line
indicates values in a sagittal image surface, and a broken line indicates
values in a meridional image surface.

[0134] Diagrams of the aberrations (a spherical aberration diagram, an
astigmatism diagram, and a distortion aberration diagram) in FIG. 6 show
that the imaging lens 20 according to the third numerical example
excellently corrects the aberrations, and has excellent image forming
performance.

[0135] Incidentally, the Abbe numbers and the focal lengths of the
respective lenses in the imaging lens 20 according to the third numerical
example are as shown in Table 9.

[0136] In FIG. 7, in which parts corresponding to those of FIG. 1 are
identified by the same reference symbols, a reference numeral 30 denotes
an imaging lens in a fourth numerical example as a whole, which has five
lenses also in this case.

[0137] The imaging lens 30 is formed by, in order from an object side, an
aperture stop STO, a first lens L31 having positive refractive power, a
second lens L32 in a meniscus shape including a concave surface facing an
image side and having negative refractive power, a third lens L33 having
positive refractive power, a fourth lens L34 in a meniscus shape
including a concave surface facing the object side and having positive
refractive power in the vicinity of an optical axis, and a fifth lens L35
having negative refractive power in the vicinity of the optical axis and
having positive refractive power in a peripheral section.

[0138] In addition, in the imaging lens 30, a seal glass SG for protecting
an image surface IMG is disposed between the fifth lens L35 and the image
surface IMG.

[0139] The aperture stop STO in the imaging lens 30 having such a
configuration is disposed in a foremost position on the object side.

[0140] Thus, in the imaging lens 30, an angle of incidence of a chief ray
of the imaging lens 30 with respect to the optical axis can be decreased
by disposing the aperture stop STO nearer to the object side than the
object side surface of the second lens L32, and bringing the position of
an exit pupil as close to the object side as possible. It is thus
possible to improve light receiving efficiency, and avoid degradation in
image quality due to color mixture.

[0141] The imaging lens 30 thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0142] Table 10 shows lens data when concrete numerical values are applied
to the imaging lens 30 according to the fourth numerical example together
with the F-number FNo, the focal length f of the entire lens system, and
the angle of view 2ω. Incidentally, the imaging lens 30 has
performance corresponding to a focal length of 30 (mm) when calculated in
terms of a 35-mm film.

[0143] In the imaging lens 30, the surface (S2) on the object side of the
first lens L31, the surface (S3) on the image side of the first lens L31,
the surface (S4) on the object side of the second lens L32, the surface
(S5) on the image side of the second lens L32, the surface (S6) on the
object side of the third lens L33, the surface (S7) on the image side of
the third lens L33, the surface (S8) on the object side of the fourth
lens L34, the surface (S9) on the image side of the fourth lens L34, the
surface (S10) on the object side of the fifth lens L35, and the surface
(S11) on the image side of the fifth lens L35 are formed in an aspheric
shape.

[0144] Next, Table 11 shows the aspheric coefficients "A," "B," "C," and
"D" of the 4th order, the 6th order, the 8th order, and the 10th order of
the aspheric surfaces in the imaging lens 30 according to the fourth
numerical example together with the conic constant "K." Incidentally,
"E-02" in Table 11 denotes an exponential representation having a base of
10, that is, "10-2."

[0145] FIG. 8 shows aberrations in the imaging lens 30 according to the
fourth numerical example. Also in this astigmatism diagram, a solid line
indicates values in a sagittal image surface, and a broken line indicates
values in a meridional image surface.

[0146] Diagrams of the aberrations (a spherical aberration diagram, an
astigmatism diagram, and a distortion aberration diagram) in FIG. 8 show
that the imaging lens 30 according to the fourth numerical example
excellently corrects the aberrations, and has excellent image forming
performance.

[0147] Incidentally, the Abbe numbers and the focal lengths of the
respective lenses in the imaging lens 30 according to the fourth
numerical example are as shown in Table 12.

[0148] In FIG. 9, in which parts corresponding to those of FIG. 1 are
identified by the same reference symbols, a reference numeral 40 denotes
an imaging lens in a fifth numerical example as a whole, which has five
lenses also in this case.

[0149] The imaging lens 40 is formed by, in order from an object side, an
aperture stop STO, a first lens L41 having positive refractive power, a
second lens L42 in a meniscus shape including a concave surface facing an
image side and having negative refractive power, a third lens L43 having
positive refractive power, a fourth lens L44 in a meniscus shape
including a concave surface facing the object side and having positive
refractive power in the vicinity of an optical axis, and a fifth lens L45
having negative refractive power in the vicinity of the optical axis and
having positive refractive power in a peripheral section.

[0150] In addition, in the imaging lens 40, a seal glass SG for protecting
an image surface IMG is disposed between the fifth lens L45 and the image
surface IMG.

[0151] The aperture stop STO in the imaging lens 40 having such a
configuration is disposed in a foremost position on the object side.

[0152] Thus, in the imaging lens 40, an angle of incidence of a chief ray
of the imaging lens 40 with respect to the optical axis can be decreased
by disposing the aperture stop STO nearer to the object side than the
object side surface of the second lens L42, and bringing the position of
an exit pupil as close to the object side as possible. It is thus
possible to improve light receiving efficiency, and avoid degradation in
image quality due to color mixture.

[0153] The imaging lens 40 thus has a five-piece configuration and a power
arrangement as described above. It is thereby possible to correct
spherical aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature, which become a problem when an aperture
is enlarged, in a well-balanced manner, while reducing a total optical
length.

[0154] Table 13 shows lens data when concrete numerical values are applied
to the imaging lens 40 according to the fifth numerical example together
with the F-number FNo, the focal length f of the entire lens system, and
the angle of view 2ω. Incidentally, the imaging lens 40 has
performance corresponding to a focal length of 34 (mm) when calculated in
terms of a 35-mm film.

[0155] In the imaging lens 40, the surface (S2) on the object side of the
first lens L41, the surface (S3) on the image side of the first lens L41,
the surface (S4) on the object side of the second lens L42, the surface
(S5) on the image side of the second lens L42, the surface (S6) on the
object side of the third lens L43, the surface (S7) on the image side of
the third lens L43, the surface (S8) on the object side of the fourth
lens L44, the surface (S9) on the image side of the fourth lens L44, the
surface (S10) on the object side of the fifth lens L45, and the surface
(S11) on the image side of the fifth lens L45 are formed in an aspheric
shape.

[0156] Next, Table 14 shows the aspheric coefficients "A," "B," "C," and
"D" of the 4th order, the 6th order, the 8th order, and the 10th order of
the aspheric surfaces in the imaging lens 40 according to the fifth
numerical example together with the conic constant "K." Incidentally,
"E-02" in Table 14 denotes an exponential representation having a base of
10, that is, "10-2."

[0157]FIG. 10 shows aberrations in the imaging lens 40 according to the
fifth numerical example. Also in this astigmatism diagram, a solid line
indicates values in a sagittal image surface, and a broken line indicates
values in a meridional image surface.

[0158] Diagrams of the aberrations (a spherical aberration diagram, an
astigmatism diagram, and a distortion aberration diagram) in FIG. 10 show
that the imaging lens 40 according to the fifth numerical example
excellently corrects the aberrations, and has excellent image forming
performance.

[0159] Incidentally, the Abbe numbers and the focal lengths of the
respective lenses in the imaging lens 40 according to the fifth numerical
example are as shown in Table 15.

[0160] Next, values in the first to fifth numerical examples which values
correspond to the conditional expressions (1) to (9) are derived on the
basis of Table 3, Table 6, Table 9, Table 12, and Table 15, and are shown
in Table 16.

[0161] According to Table 16, as shown for the conditional expression (1),
it can be seen that the Abbe numbers 11)1 at the d-line of the first
lenses L1 (FIG. 1), L11 (FIG. 3), L21 (FIG. 5), L31 (FIG. 7), and L41
(FIG. 9) in the first to fifth numerical examples are all "56.3," and
thus satisfy the conditional expression (1) ν1>50.

[0162] In addition, according to Table 16, as shown for the conditional
expression (2), it can be seen that the Abbe numbers ν2 at the d-line
of the second lenses L2 (FIG. 1), L12 (FIG. 3), L22 (FIG. 5), L32 (FIG.
7), and L42 (FIG. 9) in the first to fifth numerical examples satisfy the
conditional expression (2) ν2<30, with a maximum of "25.6" in the
first numerical example, the second numerical example, the fourth
numerical example, and the fifth numerical example.

[0163] Further, according to Table 16, as shown for the conditional
expression (3), it can be seen that the Abbe numbers ν3 at the d-line
of the third lenses L3 (FIG. 1), L13 (FIG. 3), L23 (FIG. 5), L33 (FIG.
7), and L43 (FIG. 9) in the first to fifth numerical examples are all
"56.3," and thus satisfy the conditional expression (3) ν3>50.

[0164] Further, according to Table 16, as shown for the conditional
expression (4), it can be seen that the Abbe numbers ν4 at the d-line
of the fourth lenses L4 (FIG. 1), L14 (FIG. 3), L24 (FIG. 5), L34 (FIG.
7), and L44 (FIG. 9) in the first to fifth numerical examples are all
"56.3," and thus satisfy the conditional expression (4) ν4>50.

[0165] Further, according to Table 16, as shown for the conditional
expression (5), it can be seen that "f3/f4" satisfies the
conditional expression (5) 0<f3/f4<3.0, "0.10" in the
fifth numerical example being a minimum value of f3/f4, and
"1.89" in the fourth numerical example being a maximum value of
f3/f4.

[0166] Further, according to Table 16, as shown for the conditional
expression (6), it can be seen that "|f1/f2|" satisfies the
conditional expression (6) 0.5<|f1/f2|<1.3, "0.59" in the
fourth numerical example being a minimum value of |f1/f2|, and
"1.09" in the second numerical example being a maximum value of
|f1/f2|.

[0167] Further, according to Table 16, it can be seen that while "0.59" in
the fourth numerical example and "1.09" in the second numerical example
fall outside the numerical value range of the conditional expression (7)
0.6<|f1/f2|<1.0, the conditional expression (7) is
satisfied in the first numerical example, the third numerical example,
and the fifth numerical example excluding the fourth numerical example
and the second numerical example, "0.75" in the third numerical example
being a minimum value, and "0.88" in the first numerical example being a
maximum value, as shown for the conditional expression (7).

[0168] Thus, as shown in the aberration diagrams of FIG. 2, FIG. 6, and
FIG. 10, the imaging lens 1 according to the first numerical example, the
imaging lens 20 according to the third numerical example, and the imaging
lens 40 according to the fifth numerical example correct aberrations more
excellently, and have more excellent image forming performance than the
imaging lens 10 according to the second numerical example and the imaging
lens 30 according to the fourth numerical example shown in FIG. 4 and
FIG. 8.

[0169] Incidentally, "1.09" in the second numerical example and "0.59" in
the fourth numerical example falling outside the numerical value range of
the conditional expression (7) in Table 16 are shown in parentheses.

[0170] Further, according to Table 16, as shown for the conditional
expression (8), it can be seen that "|f5/f|" satisfies the
conditional expression (8) 0.5<|f5/f|<3.0, "0.76" in the first
numerical example being a minimum value of |f5/f|, and "1.99" in the
fifth numerical example being a maximum value of |f5/f|.

[0171] Finally, according to Table 16, as shown for the conditional
expression (9), it can be seen that the Abbe numbers ν5 at the d-line
of the fifth lenses L5 (FIG. 1), L15 (FIG. 3), L25 (FIG. 5), L35 (FIG.
7), and L45 (FIG. 9) in the first to fifth numerical examples are all
"56.3," and thus satisfy the conditional expression (9) ν5>50.

[0172] The imaging lenses 1, 10, 20, 30, and 40 in the first to fifth
numerical examples therefore satisfy the conditional expressions (1) to
(6), the conditional expression (8), and the conditional expression (9)
described above.

[0173] In addition, the imaging lenses 1, 20, and 40 in the first
numerical example and the third to fifth numerical examples excluding the
second numerical example and the fourth numerical example satisfy all of
the conditional expressions (1) to (9) described above.

[0174] Thus, the imaging lenses 1, 10, 20, 30, and 40 in the first to
fifth numerical examples can excellently correct spherical aberration of
axial aberrations, comatic aberration of off-axis aberrations, and field
curvature, and have optical performance that can sufficiently correspond
with a high pixel imaging element having eight million pixels or more,
for example, when the aperture is enlarged to an F-number of about 2.0.

[0175] In addition, the imaging lenses 1, 10, 20, 30, and 40 in the first
to fifth numerical examples can excellently correct axial chromatic
aberration while the total optical length is reduced, and have high
resolution performance necessary as the aperture is enlarged to an
F-number of about 2.0.

3. IMAGING DEVICE AND PORTABLE TELEPHONE

3-1. Configuration of Imaging Device

[0176] Description will next be made of an imaging device having a
configuration formed by combining the imaging lens according to the
present invention with an imaging element such for example as a CCD
(Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide
Semiconductor) sensor for converting an optical image formed by the
imaging lens into an electric signal.

[0177] Incidentally, the following description will be made of an imaging
device to which an imaging lens having an aperture stop disposed in a
foremost position on an object side (for example the imaging lens 1 in
the foregoing first numerical example) is applied. However, an imaging
lens having an aperture stop disposed between a first lens and a second
lens, such as the imaging lens 10 in the foregoing second numerical
example (FIG. 3), can also be similarly applied to an imaging device.
Incidentally, the imaging lens applied to the imaging device has
performance corresponding to a range of 24 to 40 (mm) as focal length of
the entire lens system when calculated in terms of a 35-mm film.

[0178] The imaging lens provided to the imaging device is formed by, in
order from an object side, an aperture stop, a first lens having positive
refractive power, a second lens in a meniscus shape including a concave
surface facing an image side and having negative refractive power, a
third lens having positive refractive power, a fourth lens in a meniscus
shape including a concave surface facing the object side and having
positive refractive power in the vicinity of an optical axis, and a fifth
lens having negative refractive power in the vicinity of the optical axis
and having positive refractive power in a peripheral section.

[0179] The imaging lens in the imaging device thus has a five-piece
configuration and a power arrangement as described above. It is thereby
possible to correct spherical aberration of axial aberrations, comatic
aberration of off-axis aberrations, and field curvature, which become a
problem when an aperture is enlarged, in a well-balanced manner, while
reducing a total optical length.

[0180] The aperture stop in the imaging lens of the imaging device having
such a configuration is disposed in a foremost position on the object
side.

[0181] Thus, in the imaging lens of the imaging device, an angle of
incidence of a chief ray of the imaging lens with respect to the optical
axis can be decreased by disposing the aperture stop nearer to the object
side than the object side surface of the second lens, and bringing the
position of an exit pupil as close to the object side as possible. It is
thus possible to improve light receiving efficiency, and avoid
degradation in image quality due to color mixture.

[0182] In addition, all of the first to fifth lenses of the imaging lens
in the imaging device are formed by lenses made of resin, and formed so
as to satisfy the conditional expression (1), the conditional expression
(2), the conditional expression (3), and the conditional expression (4)
in the following:

ν1>50 (1)

ν2<30 (2)

ν3>50 (3)

ν4>50 (4)

where ν1 is the Abbe number of the first lens at the d-line
(wavelength of 587.6 nm), ν2 is the Abbe number of the second lens at
the d-line (wavelength of 587.6 nm), ν3 is the Abbe number of the
third lens at the d-line (wavelength of 587.6 nm), and ν4 is the Abbe
number of the fourth lens at the d-line (wavelength of 587.6 nm).

[0183] The conditional expression (1) defines the Abbe number of the first
lens at the d-line. The conditional expression (2) defines the Abbe
number of the second lens at the d-line. The conditional expression (3)
defines the Abbe number of the third lens at the d-line. The conditional
expression (4) defines the Abbe number of the fourth lens at the d-line.
The conditional expressions represent conditions for excellently
correcting chromatic aberration occurring in the lens system.

[0184] When the imaging lens deviates from the specified values of the
conditional expression (1), the conditional expression (2), the
conditional expression (3), and the conditional expression (4), the
correction of axial chromatic aberration, which is necessary in enlarging
the aperture with an F-number of about 2.0, becomes difficult.

[0186] Further, because all the lenses of the imaging lens in the imaging
device are formed by lenses made of resin as a same material, amounts of
change in refractive power in all the lenses at a time of a variation in
temperature can be made to be uniform, and thus variation in field
curvature, which becomes a problem at a time of a variation in
temperature, can be suppressed.

[0187] In addition, because all of the lenses of the imaging lens in the
imaging device are formed by inexpensive and lightweight lenses made of
resin, the imaging lens as a whole can be reduced in weight while mass
productivity is ensured.

[0188] Further, the imaging lens in the imaging device is formed so as to
satisfy a conditional expression (5) in the following:

0<f3/f4<3.0 (5)

where f3 is the focal length of the third lens, and f4 is the
focal length of the fourth lens.

[0189] The conditional expression (5) defines a ratio between the focal
length f3 of the third lens and the focal length f4 of the
fourth lens, and limits a balance between the refractive power of the
third lens and the refractive power of the fourth lens.

[0190] When the imaging lens in the imaging device deviates from the upper
limit value of the conditional expression (5), the power (refractive
power) of the third lens becomes too weak, and the correction of axial
chromatic aberration becomes difficult, so that excellent optical
performance cannot be maintained. When the imaging lens deviates from the
lower limit value, on the other hand, the power of the third lens becomes
strong, which is advantageous in terms of aberration correction, but the
power of the fourth lens becomes too weak, and the total optical length
is increased, so that the miniaturization of the present lens system
becomes difficult.

[0191] Thus, in the imaging lens of the imaging device, by satisfying the
conditional expression (5), it is possible to reduce the total optical
length while effectively correcting axial chromatic aberration and
ensuring excellent optical performance.

[0192] Further, the imaging lens in the imaging device is formed so as to
satisfy a conditional expression (6) in the following:

0.5<|f1/f2|<1.3 (6)

where f1 is the focal length of the first lens, and f2 is the
focal length of the second lens.

[0193] The conditional expression (6) defines a ratio between the focal
length f1 of the first lens and the focal length f2 of the
second lens, and limits a balance between the refractive power of the
first lens and the refractive power of the second lens.

[0194] When the imaging lens in the imaging device deviates from the upper
limit value of the conditional expression (6), the power of the second
lens becomes strong, which is advantageous in terms of aberration
correction, but the power of the second lens becomes too strong, and the
total optical length is increased, so that the miniaturization of the
present lens system becomes difficult. When the imaging lens deviates
from the lower limit value, on the other hand, the power of the second
lens becomes too weak, and the correction of axial chromatic aberration
becomes difficult, so that excellent optical performance cannot be
maintained.

[0195] Thus, in the imaging lens of the imaging device, by satisfying the
conditional expression (6), it is possible to reduce the total optical
length while effectively correcting axial chromatic aberration and
ensuring excellent optical performance.

[0196] Further, the conditional expression (6) is desirably set so as to
satisfy a range shown in a conditional expression (7).

0.6<|f1/f2|<1.0 (7)

[0197] Thus, in the imaging lens of the imaging device, by satisfying the
conditional expression (7), the reduction of the total optical length and
the correction of axial chromatic aberration can be achieved in a better
balanced manner.

[0198] Further, the imaging lens in the imaging device is formed to
satisfy a conditional expression (8) and a conditional expression (9) in
the following:

0.5<|f5/f|<3.0 (8)

ν5>50 (9)

where f is the focal length of the entire lens system, f5 is the
focal length of the fifth lens, and ν5 is the Abbe number of the fifth
lens at the d-line (wavelength of 587.6 nm).

[0199] The conditional expression (8) defines a ratio between the focal
length f5 of the fifth lens and the focal length f of the entire
lens system, and limits the power of the fifth lens.

[0200] When the imaging lens in the imaging device deviates from the upper
limit value of the conditional expression (8), the power of the fifth
lens becomes weak, which is advantageous in terms of aberration
correction, but the total optical length is increased, so that the
miniaturization of the present lens system becomes difficult. When the
imaging lens deviates from the lower limit value, on the other hand, the
power of the fifth lens becomes too strong, and it becomes difficult to
correct field curvature occurring from a center to an intermediate image
height (for example a height increased by 20 to 50 percent) in a
well-balanced manner.

[0201] The conditional expression (9) defines the Abbe number of the fifth
lens at the d-line. When the Abbe number falls below the specified value,
it becomes difficult to correct axial chromatic aberration and chromatic
aberration of magnification in a well-balanced manner, and excellent
optical performance cannot be maintained.

[0202] Thus, in the imaging lens of the imaging device, by satisfying the
conditional expression (8) and the conditional expression (9), it is
possible to reduce the total optical length while correcting axial
chromatic aberration and chromatic aberration of magnification in a
well-balanced manner and ensuring excellent optical performance
corresponding with a high pixel imaging element.

[0203] Thus, the imaging lens of the imaging device according to the
present invention has excellent optical performance, with spherical
aberration of axial aberrations, comatic aberration of off-axis
aberrations, and field curvature corrected in a well-balanced manner, for
a high pixel imaging element having eight million pixels or more, for
example, even when the aperture is enlarged to an F-number of about 2.0.

[0204] In addition, in the present invention, the imaging device including
a small-size and large-aperture imaging lens having high resolution
performance with axial chromatic aberration corrected in a well-balanced
manner while the total optical length is reduced can be formed for a high
pixel imaging element having eight million pixels or more, for example.

[0205] Further, because all of the lenses of the imaging lens in the
imaging device are formed by inexpensive lenses made of resin, variation
in field curvature, which becomes a problem at a time of a variation in
temperature, can be suppressed while mass productivity is ensured.

3-2. Configuration of Portable Telephone Including Imaging Device

[0206] Description will next be made of a portable telephone including the
imaging device according to the present invention.

[0207] As shown in FIG. 11 and FIG. 12, the portable telephone 100 has a
display section 101 and a main body section 102 foldably coupled to each
other via a hinge part 103. The display section 101 and the main body
section 102 are in a folded state when the portable telephone 100 is
carried (FIG. 11). The display section 101 and the main body section 102
are in an unfolded state when the portable telephone 100 is used during a
call (FIG. 12).

[0208] The display section 101 has a liquid crystal display panel 111
disposed in one surface of the display section 101, and has a speaker 112
disposed above the liquid crystal display panel 111. In addition, an
imaging device 107 is incorporated within the display section 101, and an
infrared communicating section 104 for performing infrared wireless
communication is disposed at an end of the display section 101.

[0209] In addition, a cover lens 105 located on the object side of the
first lens in the imaging device 107 is disposed in another surface of
the display section 101.

[0210] The main body section 102 has various kinds of operating keys 113
such as numeric keys, a power key, and the like disposed in one surface
of the main body section 102, and has a microphone 114 disposed at a
lower end of the main body section 102. The main body section 102 also
has a memory card slot 106 disposed in a side of the main body section
102. A memory card 120 can be inserted into and removed from the memory
card slot 106.

[0211] As shown in FIG. 13, the portable telephone 100 has a CPU (Central
Processing Unit) 130. The portable telephone 100 expands a control
program stored in a ROM (Read Only Memory) 131 into a RAM (Random Access
Memory) 132. The portable telephone 100 performs centralized control of
the portable telephone 100 as a whole via a bus 133.

[0212] The portable telephone 100 has a camera control section 140. The
portable telephone 100 can photograph a still image or a moving image by
controlling the imaging device 107 via the camera control section 140.

[0213] The camera control section 140 subjects image data obtained by
photographing via the imaging device 107 to compression processing by
JPEG (Joint Photographic Experts Group), MPEG (Moving Picture Expert
Group), or the like, and sends out the resulting image data to the CPU
130, a display control section 134, a communication control section 160,
a memory card interface 170, or an infrared interface 135 via the bus
133.

[0214] The imaging device 107 is formed by combining one of the imaging
lenses 1, 10, 20, 30, and 40 with an imaging element SS formed by a CCD
sensor, a CMOS sensor, or the like.

[0215] The CPU 130 in the portable telephone 100 temporarily stores the
image data supplied from the camera control section 140 in the RAM 132,
stores the image data in the memory card 120 via the memory card
interface 170 as required, or outputs the image data to the liquid
crystal display panel 111 via the display control section 134.

[0216] In addition, the portable telephone 100 can temporarily store audio
data recorded via the microphone 114 at the same time as the
photographing in the RAM 132 via an audio codec 150, store the audio data
in the memory card 120 via the memory card interface 170 as required, or
perform audio output of the audio data from the speaker 112 via the audio
codec 150 simultaneously with image display on the liquid crystal display
panel 111.

[0217] Incidentally, the portable telephone 100 can output the image data
and the audio data to the outside via the infrared interface 135 and the
infrared communicating section 104 to transmit the image data and the
audio data to another electronic device having an infrared communicating
function such for example as a portable telephone, a personal computer,
or a PDA (Personal Digital Assistant).

[0218] Incidentally, in the portable telephone 100, when the moving image
or the still image is to be displayed on the liquid crystal display panel
111 on the basis of the image data stored in the RAM 132 or the memory
card 120, the image data is decoded and decompressed by the camera
control section 140, and thereafter output to the liquid crystal display
panel 111 via the display control section 134.

[0219] The communication control section 160 transmits and receives radio
waves to and from a base station via an antenna not shown in the figures.
The communication control section 160 in a voice call mode subjects
received audio data to predetermined processing, and thereafter outputs
the audio data to the speaker 112 via the audio codec 150.

[0220] In addition, the communication control section 160 subjects an
audio signal obtained by collecting sound by the microphone 114 to
predetermined processing via the audio codec 150, and thereafter
transmits the audio signal via the antenna not shown in the figures.

[0221] The imaging lens 1, 10, 20, 30, or 40 incorporated within the
imaging device 107 can be miniaturized and have a large aperture while
the total optical length is reduced, as described above. The imaging
device 107 is therefore advantageous when incorporated in an electronic
device desired to be reduced in size, such as a portable telephone or the
like.

4. OTHER EMBODIMENTS

[0222] Incidentally, in the foregoing embodiment, the concrete shapes,
structures, and numerical values of the respective parts in the imaging
lenses 1, 10, 20, 30, and 40 as the first to fifth numerical examples
each represent a mere example of embodiment performed in carrying out the
present invention. The technical scope of the present invention should
not be construed as limited by these concrete shapes, structures, and
numerical values.

[0223] In addition, in the foregoing embodiment, description has been made
of a case where concrete numerical values in Table 16 are shown on the
basis of the first to fifth numerical examples. However, the present
invention is not limited to this. Various other concrete shapes,
structures, and numerical values may be used within such ranges as to
satisfy the conditional expressions (1) to (9).

[0224] Further, in the foregoing embodiment, description has been made of
a case where the imaging lens uses the first lens including convex
surfaces facing the object side and the image side and having positive
refractive power. However, the present invention is not limited to this.
The imaging lens may use for example a first lens in a meniscus shape
including a concave surface facing the image side and having positive
refractive power as long as only the conditional expression (1) and the
conditional expression (6) are satisfied.

[0225] Further, in the foregoing embodiment, description has been made of
a case where the imaging lens uses the third lens including convex
surfaces facing the object side and the image side and having positive
refractive power. However, the present invention is not limited to this.
The imaging lens may use for example a third lens in a meniscus shape
including a concave surface facing the object side and having positive
refractive power as long as only the conditional expression (3) and the
conditional expression (5) are satisfied.

[0226] Further, in the foregoing embodiment, description has been made of
a case where the imaging lens has the power arrangement described above,
satisfies the conditional expressions (1) to (4), the conditional
expression (5), the conditional expression (6), the conditional
expression (8), and the conditional expression (9), and has the aperture
stop STO disposed nearer to the object side than the object side surface
of the second lens.

[0227] The present invention is not limited to this. The imaging lens may
have the power arrangement described above, satisfy only the conditional
expressions (1) to (4), the conditional expression (5), and the
conditional expression (6), and have the aperture stop STO disposed
nearer to the object side than the object side surface of the second
lens.

[0228] In addition, the imaging lens may have the power arrangement
described above, satisfy only the conditional expressions (1) to (4), the
conditional expression (5), the conditional expression (8), and the
conditional expression (9), and have the aperture stop STO disposed
nearer to the object side than the object side surface of the second
lens, or may have the power arrangement described above, satisfy only the
conditional expressions (1) to (4) and the conditional expression (5),
and have the aperture stop STO disposed nearer to the object side than
the object side surface of the second lens.

[0229] Further, the imaging lens may have the power arrangement described
above, satisfy only the conditional expressions (1) to (4), the
conditional expression (6), the conditional expression (8), and the
conditional expression (9), and have the aperture stop STO disposed
nearer to the object side than the object side surface of the second
lens, or may have the power arrangement described above, satisfy only the
conditional expressions (1) to (4) and the conditional expression (6),
and have the aperture stop STO disposed nearer to the object side than
the object side surface of the second lens.

[0230] Further, the imaging lens may have the power arrangement described
above, satisfy only the conditional expressions (1) to (4), the
conditional expression (8), and the conditional expression (9), and have
the aperture stop STO disposed nearer to the object side than the object
side surface of the second lens, or may have the power arrangement
described above, satisfy only the conditional expressions (1) to (4), and
have the aperture stop STO disposed nearer to the object side than the
object side surface of the second lens.

[0231] Further, the imaging lens may have the power arrangement described
above, satisfy only the conditional expression (5), the conditional
expression (6), the conditional expression (8), and the conditional
expression (9), and have the aperture stop STO disposed nearer to the
object side than the object side surface of the second lens, or may have
the power arrangement described above, satisfy only the conditional
expression (5) and the conditional expression (6), and have the aperture
stop STO disposed nearer to the object side than the object side surface
of the second lens.

[0232] Further, the imaging lens may have the power arrangement described
above, satisfy only the conditional expression (5), the conditional
expression (8), and the conditional expression (9), and have the aperture
stop STO disposed nearer to the object side than the object side surface
of the second lens, or may have the power arrangement described above,
satisfy only the conditional expression (5), and have the aperture stop
STO disposed nearer to the object side than the object side surface of
the second lens.

[0233] Further, the imaging lens may have the power arrangement described
above, satisfy only the conditional expression (6), the conditional
expression (8), and the conditional expression (9), and have the aperture
stop STO disposed nearer to the object side than the object side surface
of the second lens, or may have the power arrangement described above,
satisfy only the conditional expression (6), and have the aperture stop
STO disposed nearer to the object side than the object side surface of
the second lens.

[0234] Further, the imaging lens may have the power arrangement described
above, satisfy only the conditional expression (8) and the conditional
expression (9), and have the aperture stop STO disposed nearer to the
object side than the object side surface of the second lens, or may have
the power arrangement described above, and have the aperture stop STO
disposed nearer to the object side than the object side surface of the
second lens.

INDUSTRIAL APPLICABILITY

[0235] In the imaging lens and the imaging device according to the present
invention, a case where the imaging device 107 is incorporated in the
portable telephone 100, for example, has been illustrated as an example.
However, applications of the imaging device are not limited to this. The
imaging device is widely applicable to various other electronic devices
such as digital video cameras, digital still cameras, personal computers
including a camera, PDAs including a camera, and the like.